Neurostimulation systems, and increasingly implantable neurostimulation systems, are used to treat various neurological diseases and other neurological disorders, such as epilepsy, movement disorders (e.g., Parkinson's disease) and chronic pain. Research is ongoing concerning use of implantable neurostimulation systems to treat psychological disorders (e.g., depression), headaches and Alzheimer's disease and to facilitate stroke recovery.
A typical neurostimulation system comprises a stimulation source, such as a pulse generator, that provides stimulation to target neural tissue via one or more leads connected to the stimulation source. Each lead has one or more electrodes designed to be placed on a surface of the brain (cortical electrodes) or within the brain (deep brain electrodes). A signal is transmitted from the stimulation source to the electrode(s), and thus to the desired site in the brain. Some systems also have the capacity to detect and respond to signals detected from one or more of the electrodes through the leads (e.g., “responsive neurostimulators” or other “closed-loop” devices).
Access to the desired portion of the brain is commonly achieved by drilling a hole in a patient's skull (cranium). A cranial drill, sometimes referred to as a “burr”, is used to drill the hole through the outer table, cancellous bone, and inner table of the cranium.
A lead with one or more electrodes on its distal end is introduced into the burr hole and manipulated from outside the patient until the electrodes are positioned at the desired location. Leads with cortical strip electrodes are designed to lay on a surface of the brain. The location at which a cortical strip electrode is placed, for example, may correspond to an area of brain tissue which has previously been identified as the likely focus of seizure activity, for example, using magnetic resonance imaging or some other diagnostic or clinical procedure. Leads with deep brain electrodes are designed to be pushed at least partly into the brain tissue, so that the electrodes rest at or near a target structure (e.g., hypothalamus, subthalamic nucleus, etc.).
Maintaining the electrodes at the desired location once the leads have been implanted is often important relative to the purpose of the implant (e.g., delivering stimulation therapy, monitoring a sensed brain signal, etc.). Thus, once one or more leads are placed in the desired areas on in the brain, the proximal portions of the leads (i.e., a portion of each lead that extends away from the implant site and exteriorly of the burr hole) commonly are secured to prevent the electrodes from being inadvertently dislodged or otherwise moving too much from the location at which the distal ends of the leads bearing the electrodes have been placed. One or all of the components that are used to secure the leads at the site of the burr hole commonly are put into place in the burr hole before the leads are implanted.
Sometimes, the leads are permitted some play or give after they have been secured, to allow for some relative movement of the leads and the brain or skull, for example, during some sort or head trauma. A device used to secure the proximal portions of the leads also often is provided with a feature that allows the hole to be sealed or substantially sealed to minimize infection from outside agents, such as a cap with a slot through which the leads can be extended and then routed to measuring or stimulation components.
Lead fixation devices commonly are comprised of multiple parts that are assembled in the operating room by the surgeon, require neurosurgical screws to secure, and are made partially or wholly of rigid materials.